1. Field of the Invention
The present invention relates to a gas separator for gas separation, a method for preparing the gas separator, and a method of performing gas separation.
2. Description of the Related Art
It has been determined that there are limits to the compressibility of gas molecules, a fact which is commonly known as the law of incompressibility of matter. Based on this law, it has further been found that gas molecules behave as if they have some minimum diameter, known as their xe2x80x9cworking diameterxe2x80x9d.
If it is desired to separate one species of gas from others, for any one of many reasons (e.g., enhanced combustion, gas recovery, pollution control, etc.), it has been realized for some time that the ideal separation mechanism would pass one gaseous component in a mixture, while rejecting all others in a continuous steady-state manner. Organic membrane materials allow the passage of only certain molecules, but this passage is typically controlled by a solution diffusion mechanism, which is too slow (partition coefficients allow flows of 2-3 l/ft2/day which are insufficient) a process for this approach to be used in many industrial gas separation applications. Other approaches have created xe2x80x9cmolecular sievesxe2x80x9d that capture molecules based on their size or other physical or chemical properties. Such xe2x80x9csievesxe2x80x9d are not truly sieves at all in the customary sense of the term, because no molecules pass through them. Rather, the trapped molecules must be xe2x80x9ccleaned outxe2x80x9d of these devices periodically by changes in temperature or pressure.
Previous methods to circumvent these drawbacks by the use of porous inorganic structures have focused on producing a porous material with holes in the size range of gas molecules. However, these methods have never attempted to create holes of a specific size, and for the specific purpose of separating two or more well-defined gases. Furthermore, there has been nothing in previous approaches that included the steps of first, selecting the hole size desired, and second, creating a porous material containing this hole size.
It is an object of this invention to provide a process for producing gas separation membranes having high selectivity achieved by having controlled pore sizes and narrow pore size distributions, and high permeance, defined as flux/pressure drop, achieved by having a large volume fraction porosity and a very thin selective layer.
It is yet another object of this invention to provide a process for producing gas separators using cage-like molecules to form pores. Since the size and concentration of the cage-like molecules are under the complete control of the Experimenter, the pore size and distribution of the gas separator can be tailored to separate virtually any mixture of gases in an efficient manner.
Working diameters of selected gas molecules are shown in Table 1. If the goal is, for example, to separate oxygen from nitrogen, one would need to create a porous structure, or true molecular sieve, containing holes greater than 3.5 xc3x85, but less than 3.6 xc3x85, in diameter. More correctly, the gas separator would require that one dimension of its holes be between these two numbers; the maximum dimension of the holes could be appreciably larger, because a gas molecule with a working diameter of 3.6 xc3x85, such as nitrogen, could not fit through any hole whose smaller dimension were smaller than this value. The ability to select hole sizes within a gas separator is a feature of this invention.